Printed circuit boards are utilized in a wide variety of electronics applications. Such boards comprise a circuit in which the interconnecting wires have been replaced by conductive strips printed, etched, or otherwise applied to an insulative baseboard. The various components are typically located on only one side of the baseboard. Printed circuit boards are usually manufactured as subassemblies which are then tested for electrical continuity, etc., before shipment to the customer for installation.
A variety of test fixtures have been available heretofore for testing printed circuit boards. For example, the Ostby and Barton Company of Warwick, R.I., is one source of such equipment. the printed circuit board to be tested is generally mounted over an opening in a movable platen forming the top of the unit. The top platen is spring-mounted and a vacuum chamber is defined below the platen. When vacuum is applied to the chamber, the platen moves downwardly drawing the bottom side of the printed circuit board into contact with underlying test probes to effect testing of the entire board.
Both vacuum and pressure have been utilized to bias the platen and circuit board downwardly into engagement with the test probes. U.S. Pat. Nos. 4,344,033 and 3,757,219 are representative of the prior art in this particular respect. in addition, U.S. Pat. No. 3,723,867 shows a test device which incorporates an expandable bellows for moving a printed circuit board into and out of test position. Testing has been done primarily from the bottom side of the circuit board opposite that on which the components are typically located.
Not all testing probing, however, can be conducted from the bottom sides of circuit boards, and top access test probe devices have also been available heretofore for this purpose. Top test probing is relatively more difficult due to the various sizes, shapes, and positions of components, connector blocks, etc., on the component sides of circuit boards. In bottom access testing, the circuit board is typically movable relative to fixed probes, but top access testing usually requires probes movable relative to the circuit board.
Different forms of top access test fixtures have been available heretofore. For example, the integrated circuit test probe assembly shown in U.S. Pat. No. 4,362,991 utilizes a pair of side rails carrying a movable probe assembly which is adapted to access the various components on the board, regardless of their positions.
Another approach has been to use a moving probe block which is manually actuated into and out of engagement with contact fingers on the top side of the circuit board by means of toggle clamps. This approach, however, is not automatic and is rather cumbersome and not easily expandable for use with surface mounted devices.
Yet another approach has been to utilize a pinion gear and rack to pivotally actuate the probe block through an arc into and out of engagement with the top side of the circuit board. This device can be actuated automatically upon actuation of the primary test fixture, however, connection to the interface must be made through moving wires which are subject to bending stresses and thus eventual breakage. Further, this approach is best suited for probing contact fingers and has limited, if any, application to probing surface mounted devices.
Although various types of top access test probe fixtures have been available heretofore, drawbacks and disadvantages have been encountered with the prior devices. In addition to those referred to above, the prior devices are not especially compatible with emerging surface mounted device technology. Heretofore there has not been available a vacuum-actuated top access test probe fixture which is adapted for use with a vacuum-actuated primary fixture so that both sides of a printed circuit board can be probed for testing simultaneously without undue additional expanse and complication, while avoiding the breakage problems associated with bending lead wires. There is thus a need for such a test fixture.